Dial set for carrier or 2-wire lines



Sept. 9, 1952 w, BRANDT DIAL SET FOR CARRIER 0R z-wIRE LINES 2 SHEETS-SHEET l Filed NOV. 5, 1949 Sept. 9, 1952 w. BRANDT 2,610,256

DIAL SET FOR CARRIER OR 2*WIRE LINES Filed Nov. 5, 1:,49 2 SHEETS- SHEET 2 Patented Sept. 9, 1952 DIALVSET FOR CARRIER R 2-WIRE LINES Walter Brandt,` Jersey City, N. J., assigner to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application November 5, 1949, Serial No. 125,809

14 claims. (c1.l 179-84) The present invention relates to switching arrangements for one or two Way communication systems in which` a connection between two lines is to be established `and dissolved in response to signals larriving over one or the other line.

The general object of the invention is to provide, in a communication system, switching means responsive to two signal frequencies transmitted in bothdirections over the communication channel interconnecting the two lines; another object resides in the provision of means for preventing the signal frequencies from reaching the. subscribers connected to the lines and for avoiding false operation due to speech w-aves, where the system is used for telephone communication purposes and the signal frequencies are within the band of voice frequencies transmitted.

\ According to the invention,;the two signal frem quencies are continuously transmitted from a respective end of the communication channel to the other until a supervisory signal received over one line, indicating an incoming call, interrupts the signal frequencyat the corresponding end, thereby initiating switching operations at the other end which extend the call over the second l line, whereupon a second supervisory signal, re-

ceivedover the second line to indicate the establishment of a connection, interrupts the other signal frequency, thereby initiating switching operations at the-first end to transmit an indication of the completion of the connection over the first line.

If the invention isapplied to a telephone sys tem, filter means should be provided for preventing `the signal frequencies from proceeding over the lines toward the subscriber stations and `for preventing voicefrequencies transmitted over the line from causing false operation, and the switching arrangement'is preferably designed in such manner as to take the filter means out of v,the system, as long as a conversation is carried on between the two subscribers. Special safeguards may further be provided to enable the system to be restored to normal by the reception'oi a further supervisory signal through the use of the same signal frequencies without, however, permitting the voice frequencies to cause lation, and the arrangement may be designed to give control over the establishment of a connection to the station or exchange which first seizes a line associated therewith while allowing the connection to bebroken down from either end.

The invention will bedescribed with 4reference to a twoway trunk line extending between two` carrier terminals eachlocatedadjacent a respective selector, such a system being shown in the accompanying drawing inwhch: Fig.` 1 shows so muchiof the equipment of a first station, located at the Westend of thetrunk line, as `is necessary` for an understanding of the invention; and ,n r i i Fig. 2 shows the corresponding equipment of a second station, located at the east end of the line.

The conventional parts of the west station, shown in Fig. l, include a selector SSi, a selector SSz-and a carrier terminal lCT. Selector SS1 may be the first selector ior calls proceedingA from` of selector SSl` and in parallel therewith, the.

banks A2 and B2 of selector SSz; the test banks T1, T2 of these selectors have only their con- `ventional functions and their complete circuits have not been shown. 3

Conductor TLA is connected to the A1 bank of selector SST by wayof -anarmature har! and back contact of al relay I-IAl., a band stop filter BS, another back contact and armature han of the same relay, a condenser ,C4 and a conductor TLA1; and tothe A2 bank of SS; by waypf a condenser Cs, connected to the" armature han, and a conductor TLAz; Similarly, conductor TLB is connected to theBi bank'of SSi `by way of an armature `bari-i andback contact of relay HAR, iter BS, another back contact and armature ha1`3 of the same relay a condenser C5 and a conductor TLBi; andto the B2 bank of SSz by way of a condenser C1, connected to the armature har3, and a conductor TLB2. Condensers C4, Csare also connected to the front contact of armature hart, and condensers CadCi` are also connected to the iront contact of varmature hard.

The winding ofurelay HARis connectable between a battery BA1V and ground by way` of a front contact and armature arl `of a relay AR `and Aa fro-nt contact and armature pf2 of a twowinding relay PR.; an` alternative circuit leads `from armature arl over a` front contact and sistor R1.

leads from battery BA2 to ground over an armature hard and front contact of relay HAR.

A third armature @r3 of relay VR is adapted to close over its front contactpan energizing circuit for a slow releasing relay HBRWhich lead-Sironi Y.

a battery BAS to ground over a-backcontactf and 1 l armature dri of the relay DR. A battery, not" shown, is connected. in cfolivention'alY manner across the conductors LA and LB with suoli po#A larity that relay DR will not be opera-ted when the west line is seized by selector S82 and when the 'armature a?? of relay AR engages yits front contact .under circumstances subsequently set forth.. The winding of .relay DR is shunted by. Y

tbe 'arinaturehbr and front contact and armature a2'2 being shunted .by a front Contact and armatura/urli of relay VR.

The output of the first oscillator O1, having a frequency F1, is applied via a transformer TR1, a back contact and armature dri of 'relay DR, an

armature prl and back contact of relay PR, a

band pass filter .BPL ytuned to frequency F1, and a transformer TRi to the line formed by the conductors TLA and TLB. The Vback contact of pri 1 is also connected to an armaturehur of relay HAR the `front contact of which is connected by .i

The back contact of armature hbrl is further connected to the primary of a transformer TRz the secondary of which works intothe grid circuit of a vacuum tube V1 having va cathode' re- Tlie Yplate of tube V1 is connected to the positive terminal vof afbattery BAs by way of a resistor R2 in series with a 'resonant circuit C1L1, and is furtherconnected over-a back contact and armature hdr of relay'I-IAR, acoupling condenser Gz'and a rectifier RE to the grid of a second vacuum tube V2. The rectifier RE forms part of a `biasing network for tubeVz, including resistors ARsyRs and a condenser C3, andis poled insuch a'way as to place a negative bias on the grid of that 4tube when alternating voltages are applied acrossthe biasing network. The plate of tube V2 'isfconnected to its vsource of potential BA4 through the winding of relay AR.

A front contact of armature har is connected to the junction of resistor R2 with the resonant circuit L1C1, the latter being tuned to the dierence frequency AF of the frequencies F1 and F2. Band stop 'filter -BS is tuned to the band of frequencies which 'lies between and including F1 and F2. -v

The circuits at the other end of the trunk line TL, shown in Figi 2, are identical with thosel of Fig; 1 and corresponding elements thereof have been given the same reference characters asin Fig. 1 but have been primed for'distnction; the conventional parts of the vequipment of the east station thus include a carrier terminal'CT', a selector S51' 'which may be ythe first selector for 4 calls proceeding in the east-west direction, and a selector SS2' which may be the second selector for calls coming from the west. OscillatorV O1 produces, however, the frequency F2 which is also the pass,v frequency of lter BPi', while oscilu lator O2' produces the frequency F1 to which the filter BP2 is tuned. The frequency band elimimated' by the two filters BS vand BS is the same.

The operation* of the circuit arrangement shown in Figs. 1 and 2 will now be described in connection with a call assumed to originate with a subscriber connected to the West line.

As long as theV equipment is idle, oscillator O transmits frequencyrlli to the east station over transformer ,TRnqarmatures dr! and prl, filter B'Pi, transformer TRA, west carrier terminal CT, line ',ILyeastV carrier terminal CT', transformer TRL filter BP2', armature hbrl and transformer TR3*; the oscillations are thus applied to the tube V1' and thence, Via armature hart', to tube V2" whichV thereby is biased negatively, thus'preventing `the .flow of current through the latter tube and maintaining the relay AR unoperated.

In analogous manner the frequen'cy F2 -istrans'- mitted by the oscillator O1 to theweststation and blocks the 'tubeVa .thereby maintaining .the relay AR unoperated. y

Thefrequencies'Fi and F2 may have t-lreyalues of 1750 and 19'001cycles per second, for example, When the selector SE1 is stepped by dial pulses fronla calling subscriber lto seizethe line TLA1, TLB1, a loop .is closed in well knowndnarmer .for the windings or relay PR which operates and at pri breaks the output circuit kof oscillator 01, thus discontinuing the transmission of-frequency F1 to the eastistatio'rr kAt the latter station Vthe bias of tubeV2" .disappears and relay AR operates, Vpreparing at m2 a loop for the operation of a relay (not shown) which Vis'connected across conductors LA', LB in similar manner as the relay PR is connected across conductors TLA1, TLB1, and which thus .operates when the selector .SS2 seizes the east line, 'thereby extendingthe 'call to the called subscriber'or toanoth'er selector.'Y f

At the west end 'the relaylPR responds to the next trainof dial pulses and interrupts the .free quency F11 in step therewith, Vso that the pulse-s 'are repeated by the relayAR.. The vfirst digit following the seizure of the Ytrunk lineTLisl 'thus p applied to the selector SS2 Vwhich isxstepped` lin well known manner to seize the eastline'iandrany subsequent digit is transmitted toward the east by the opening and closing .of the'aforementione'd loop formed by the armature mi' of relay AR. L, will be noted that thewindin'g ofrelay DR is included in this loop, but itsipolaritylis such that it will not operate at this sta-ge'. Y f Y When 'the' connection is'establishedl, aring signal is given tothe called subscriber an'd is heard Ythe calling subscriber 4in the Vusual manner, the frequency of this signal Ybeing Voutside the stop band of l'ilters'BS and BS. These g'ilters o`n the other hand, prevent the' frequencies VF1 and F2 from reaching the lines BALB and LA', LB' and in particular prevent thelflrequency F2, which is still on, from being heard bythe calling subscriber. -At the same time `freduency capable of passing the band pass filtersv and originating, say, at the calling end cannot'go beyond the ilters BS to cause 'false operation-so' that Vcom-- plete speech immunity of the switching arrangement is assured.

` preceding the switch SSi.

VarZ and relay DR is reversed, in well known manner, sothat the relay DR operates and at val1-I'l disconnects oscillator O1 from the system,

Y F2 to the west station. There the bias of tube V2 disappears, relay AR operates, and relay HAR is energized over prZ up and arl up. Armature hare makes its front contact and energizes relay VR which at or! and lJ1-2 reverses the current through the windings of relay PR thereby extending the supervisorysignal from the called subscriber to the calling subscriber or to any additional selector Armatures han, harZ, harB and harll take the band stop iilter BS out of the circuit.

At the `east station the operation of relay DR energizes relay HAR over prZ, dr2 up, arl up. The operation of relay VR' remains without effect since relay PR is not energized, but armatures harl, han', har3 and hard' take the band stop filter BS out of the circuit. Hence the conversation can now proceed without being impeded by these filters. t

`At the' west station the energization of relay HAR hasconnected the primary of transformer TRa to the output of band pass filter BPi over har'l up and at harB up has changed the output connections of tube V1 insueh manner that the biasing network of tube V2 is now only connected across the tuned circuit L1 C1 which presents a low impedance to oscillations of frequency F1 or F2. Preferably, the difference frequency AF (150 cycles per second in the specific example given) is selected to lie below the band of frequencies which can be transmitted Without substantial attenuation over the east and West lines. Accordingly, the'speech waves traveling back and forth over the une TL will generally be unable toA set upa suiiicient bias to de-energize either relay AR or relay AR', there having been a corresponding change in the output connections of tube V1 at the west station.

lIf either subscriber terminatesV the conversation, the circuits are restored in the following mannerzjLet'us assume that the called subscriber (at the east end) puts down the receiver first. This again reverses the current through the winding of relay DR and the latter releases. Relay HBR.'4 operates over pf2', d12', 'w3' up and at librZ up closes a shunt to prevent immediate reoperation ofrelay DR if the subscriber at the east side should again lift the receiver to make a new call. Armature dri' reapplies frequency F2 from oscillator O1` to transformer TR2 while armaturehbri connect the secondary of transformer TR2 to the filterBPz, so that frequency F1 is now likewise transmitted in the east-west direction. At the `west station the two frequencies are intermodulated in the tube V1 to produce the beat frequency AF which resonates the circuit L1C1 and blocks tube V2, thereby de-energizing relay AR which in turn releases relay HAR. This occurs substantially simultaneously with the dei speech immunity being again secured by the filters. With plate resistance R2 again effectively connected in the coupling circuit between tubes Vi and V2,frequency F2 continues to bias tube V2 l vtocutoff;fsubsequently the relay VR releases and reverses the current in the west line, thereby com- `municating the end-of-conversation signal to the calling subscriber and resulting in due course in the release of relay PR. At the east station relay VR' releases after a predetermined time `and the subsequent release of relay HBR restores the circuits to normal, relay AR'having meanwhile been cie-energized by the reapplication of frequency F1 to the line at the west station.

If the conversation had been terminated by the calling subscriber (at the West end), relay PR 'would have released, energizing relay HBR over pr2, dr2, w3 up. This would have caused the application of the outputs of bo-th oscillators O1 and O2 to the line, in the same manner as previously described for the east station, and the difference frequency AF would have appeared across the tuned circuit L1C1, blocking tube V2 and releasing relays AR and HAR. At the same time the release of PR' would have brokenv the energizing circuit of relay HAR, at pf2, and the two lters BS, BS' would have been cut back into the circuit. The subsequent operation would have been similar to that previously described, except that the eventual release of VR would have de-energized relay DR and broken the loop 'across the east line, thereby communicating the end-of-conversation signal to the called subscriber.

It follows 'that the dissolution of the connection can be effected only if the simultaneous application of frequencies F1 and F2 is accompanied by the release of either PR or DR, since otherwise neither of the HBR relays will be energized and the connection will be restored immediately after cessation of the signals. Thus, if the frequency AF is accidentally produced by the intermodulation of speech waves, the re-insertion of the band stop filters will promptly remove the bias from the V2 tubes, thereby re-operating the AR and HAR relays and again disconnecting the fore eminently suitable for use with telephone communication system, preferably with systems using impulse dialing. Itis understood, however, that the invention is not restricted to this particular field of `application and that it may be employed in any system Where supervisory signals are transmitted between two sets of switching equipment.

Accordingly, while a specific embodiment of the invention has been described in detail, the same has been given merely by way of illustration and not as a limitation upon the scope of the invention as deiined in the appended claims.

What is claimed is:

1,. In a communication system, the combination with a communication channel of a first and a second set of switching equipment located at opposite ends of said channel, said first set inmission `to the opposite end,` and-'circuitmeans selectively operable to "inactivate said4 switching '1neans,v said second f set including secondi-switching `means responsive to the 'disappearance of tion'. with ai communication channel'of a .firstand a second set of switching .equipment respectively located Aat "one and theother'endpf said .channel, said first set"inc1uding a sourceof A.aj'iirst frequency and first switchingmeansfor normally applying said "frequency to j said channel for transmissionr to.said other vendsaid second set including` a source of a secondffrequency .and second switching .means for normally applying saidsecond frequency .to said Channel'for transmission to'said oneend, said-Ysecondset. further including'iirst signaling .means responsiveltosaid irst frequency vandadapted toproduce aiirst supervisory .signalupon [disappearance .of .said first frequency, saidrst-setfurther including second signaling means respcnsiveto saidsecond frequency and adapted to produce .a .second supervisory signal upon disappeaiance-off-said second frequency, said sets further including i-lrst and second circuit means, respectively, for selectively .inactivating either. of .said ,switching Y Ulea/TIS 4. The combination :according ...to 'claim 3 v`wherein each .set is ...provided 1with..tr.ansmission means connecting .the .set toa respectivesub-- scriber, further .comprising .iiltermea-nsin each of. said .transmission means .adapted to `.prevent thetransmissionof bothof 1said frequencies to said subscribers.

5The combination according to claim fl .whereineach set further. comprises respective switch-over .means controllableirom `the associated signaling meansl and from the associated vcircuit .means to .render the .respective iilter.

means ineifective in the operated. position of both said signaling means and said circuit means.

6. The combination .according .to .claim 5 wherein eachlor said switch-over means sisiadapted to render the respective signalingimeans insensitive to the reappearanceofthe frequency from the opposite set,V thereby .maintaining said .signaling means operated.

necting said rst wave generating -mea-ns vto said channel so as-:to 4'transmit'said rst frequency .to 4said other end, --secondrswitching means at said other end normally connecting said second wave generating means to said chan- .nel so as totransmitsaid second frequency to .said one end,rst circuit means at said one end adapted to .inactivate said rst switchingmeans in response to a call signal received over the incoming line,. secondcircuit means at said other i end adapted tn inactivatesaid second switching means in response to a return signal received -8 nover ithe outgoing line, rstfsignalingmeans at wsaid-"other'end responsive tosaidtliirst frequency and adaptedto transmitafirst supervisory signal `overthe outgoing 'lineupon disappearance ofssaid nrst frequency, Vwand k'second tsignaling -means at saidone en'd'responsveto said-second frequency and adapted to transmitA a'secondsupervisory sig- ^nal 'over theV incoming "line upon `-disappearance of said sec'ondifrequency. n

8. :The fccmbination `according "to .claim 7 wherein saidiirst and second signaling meansare adapted V.to` transmit supervisory jsignals which are substantially identical4 withzsaid4 call] and return signaLrespectively. i 9. Thecombination according to claim"8,iur ther 'comprising first 'and.;second.`jfiltermeans insertediin said: incoming andoutgoingilnarespectiVely; each of said 'filter means being adapted to blockbcth of saidfrequencies.

10. "Ihe combination according tojclaim 9,1further. comprisingiirst switch-over meansat. said one end controllable from saidfirst circuit means and from said second signaling means and second switch-over. means atisaid other .end controllable .other end said'fou'rth Waveigeneratingmeans stored to normal by an end-cf.connection..sig,

.nal received ovcrthe incoming line, whereby both of .said frequencies are vsimultaneously trans- .mitted to said ,other end,.and fourthswitching ymeans-at .said other Iend controllable by said vsecondsignaling.- means .to connect .said fourth Vvwave generating ymeans to` sa-id channel in reswitch-over means when operatedbeing-` adapted :to render therespectivesignaling-means insen- --sltiveto either of said frequenciesfalone but responsive. Yto -a .combination .ofv both of said ,fre-

, V.quencies "forrendering, the .respectivesWitch-over means inoperative. l Y

Y12.,.Ihe combination.- according to .claim `l1 .wherein-,each of said thirdaand fourth switching.. meansrv comprises. slowfacting means adapted .to .transmit an.end-cf,connectionsignal to .the

V.gadjacentline a .predeterminedperiod 4after the re- .spectiveswitch-.over ineanshas beenrendered inoperative.

.. 13..,In a communication system the.. combinaa tion, witha .rst line,..a.second line. andl a communication channel interconnecting.;.said lines, .of-,a instand. a seeondset .of.switchingequipkment. adjacentsaid'rst and second lineI respectively, eachof .said setsv comprising first and sec- V.ond `.wave 4Vgenerating ...means tuned to produce two different. signal frequencies, luflter :means connected Vin the adj acent line. and i adapted to. block :bot-h .of said frequencies, `first .frelay means adapted toV apply. the output-fof said :first wave generating means to said line at a point intermediate said filter means and said channel, said relay means being responsive to a call signal arriving over the adjacent line to disconnect said iirst Wave generating means from said line, second relay means adapted to transmit a call signal over the adjacent line, signal receiving means adapted to maintain said second relay means inoperative as long as a signal frequency is received from the opposite set, third relay means adapted to disconnect said first wave generating means from said line in response to a return signal arriving over the adjacent line, fourth relay vmeans responsive to the operation of both said second and either of the other two relay means for inactivating said lter means, said fourth relay means being adapted when operated to render said signal receiving means insensitive to either of the signal frequencies from the opposite set alone but responsive to a combination of both the last-mentioned frequencies to inactivate said second relay means, fifth relay means controlled by said fourth relay means when operated to respond to the release of both said first and third relay means to connect said second Wave generating means to the adjacent line, whereby both signal frequencies produceable by the set are simultaneously transmitted over said REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 199,007 Watson Jan. 8, 1878 1,688,453 Demarest Oct. 23, 1928 2,131,164 Chauveau Sept. :27, 1938 2,408,878 Preston Oct. 8, 1946 2,414,795 Brandt Jan. 28, 1947 2,433,281 Lord Dec. 23, 194'7v 2,438,902 Deloraine Apr. 6, 1948 2,454,498 Bartelink Nov. 123, 1948 

